A hometown newspaper with a local office, local owners & lots of local news
A hometown newspaper with a local office, local owners & lots of local news
This image, taken on June 19, 2018, by an astronaut onboard the International Space Station, shows sediment runoff into Lake Superior near Duluth. The Nemadji River regularly unloads red clay sediment into the Lake Superior Harbor, but the discharge was intensified during the flooding event and discolored waters. Astronaut photograph ISS056-E-21591 is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center.
Hello again from the red clay waters of the Nemadji River.
Last week we journeyed back in time and were lucky to see Glacial Lake Duluth and witness a lake 450 feet higher than current Lake Superior. It was so high it backed up and covered Jay Cooke Park and a good deal of Carlton County; it existed there for about 1,000 years, according to glacial geologists (glaciologists).
The presence of this ancient lake is an important part of the Nemadji River story. We know the Nemadji River basin has an abundance of red clay soils, hence red clay in the water. I think we should travel back in time again to see how the red clay got there in the first place, and why it is red.
I will dial my science time machine to 20,000 years ago and travel to northern Minnesota. As I step out of my machine I see ice in all directions, as far as the eye can see. To find out where the clay came from I need to travel down through the glacial ice to the bedrock it is sitting on. Luckily I brought a large melting tool that will melt a tunnel for me; this will take a while as I need to get through at least a mile of ice. As I descend I am amazed at the beautiful blue color of this ice. Sometimes I see large cracks with really cold liquid water flowing through them. I also notice some of the ice has rocks and sand and dust mixed in, then finally I reach the bedrock.
I am now standing on granite; it has pink, white, and black colors all mixed together. I notice long scratches on this granite, and I can see they are being made by rocks and gravel imbedded in the ice. As it moves like a giant piece of sandpaper, it grinds and pulverizes the granite, creating what glaciologists call rock flour. Most of this rock flour is made of particles 1,000 times smaller than a grain of sand. These particles are also slightly flattened and are pliable - this is clay.
Back to the present. Looking down on the Nemadji from a bridge on Highway 23, I am reminded of the red color of this clay.
Clay doesn't have to be red. Ask any potter, it can be white, gray, tan or red. Our clay, which came from rock flour, which came from ground granite, has some iron in it. Oxygen loves iron and will attack it when it can find it; that is what happened: the iron rusted or, as scientists say, it oxidized. Oxidized iron is red, like some parts of my '97 Toyota.
Next time you get a chance to look at the Nemadji River, "the river on the left" in Ojibwe, remember the great story it has to tell.
Curiosity may kill the cat, but it enriches the human. Keep wondering.
FDLTCC science tutor Glen Sorenson was Minnesota Teacher of the Year before he retired from teaching science at Proctor High School after 30-plus years. He is an avid outdoorsman who most recently coached the Lumberjacks Nordic ski team.
